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lecture10 - 1 Physics 2102 Gabriela González • Any two...

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Unformatted text preview: 1 Physics 2102 Gabriela González • Any two charged conductors form a capacitor. •Capacitance : C= Q/V •Simple Capacitors: Parallel plates : C = ε A/d Spherical : C = ε 0 4 π ab/(b-a) Cylindrical : C = ε 0 2 π L/ln(b/a) 2 • Start out with uncharged capacitor • Transfer small amount of charge dq from one plate to the other until charge on each plate has magnitude Q • How much work was needed? dq • Energy stored in capacitor:U = Q 2 /(2C) = CV 2 /2 • View the energy as stored in ELECTRIC FIELD • For example, parallel plate capacitor: Energy DENSITY = energy/volume = u = volume = Ad General expression for any region with vacuum (or air) 3 • If the space between capacitor plates is filled by a dielectric, the capacitance INCREASES by a factor κ • This is a useful, working definition for dielectric constant. • Typical values of κ : 10 - 200 +Q - Q DIELECTRIC C = κε A/d • Capacitor has charge Q, voltage V • Battery remains connected while dielectric slab is inserted. • Do the following increase, decrease or stay the same: – Potential difference? – Capacitance? – Charge? – Electric field? dielectric slab 3 • If the space between capacitor plates is filled by a dielectric, the capacitance INCREASES by a factor κ • This is a useful, working definition for dielectric constant. • Typical values of κ : 10 - 200 +Q - Q DIELECTRIC C = κε A/d • Capacitor has charge Q, voltage V • Battery remains connected while dielectric slab is inserted....
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This note was uploaded on 05/20/2011 for the course PHYS 2102 taught by Professor Gimmnaco during the Fall '08 term at LSU.

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lecture10 - 1 Physics 2102 Gabriela González • Any two...

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